This invention relates to electric-actuated emission control valves of automotive vehicles, especially to a valve that comprises a non-magnetic sleeve that guides motion of a magnetic armature that controls the extent to which the valve selectively restricts a flow passage.
Controlled engine exhaust gas recirculation (EGR) is a known technique for reducing oxides of nitrogen in products of combustion that are exhausted from an internal combustion engine to atmosphere. A known EGR system comprises an EGR valve that is controlled in accordance with engine operating conditions to regulate the amount of engine exhaust gas that is recirculated to the induction fuel-air flow entering the engine for combustion so as to limit the combustion temperature and hence reduce the formation of oxides of nitrogen.
Electric-actuated EGR valves (EEGR valves) are capable of controlling recirculation of exhaust gas with the precision needed to comply with relevant emission regulations. However, increasingly stringent regulations create need for further improvements in EEGR valves. An EEGR valve that possesses more accurate and quicker response can be advantageous in achieving improved control of tailpipe emissions, improved driveability, and/or improved fuel economy for a vehicle having an internal combustion engine that is equipped with an EGR system.
A known electric actuator for a valve, such as an emission control valve, is a solenoid actuator having an armature that is selectively positioned along an axis according to the extent to which an electric coil of the actuator is energized by electric current. Various patents disclose emission control valves having linear solenoid actuators for improved accuracy in positioning the armature. Where the armature travel is guided by some sort of guide, frictional forces can affect positioning accuracy. In certain actuators, the armature is guided by a non-ferromagnetic sleeve that spaces the armature from surrounding stator structure of the solenoid. The armature is in surface-to-surface contact with the guide sleeve that provides a close sliding fit of the armature within the guide sleeve. Various patents show arrangements for guiding an armature within a solenoid to reduce sliding friction, but they may involve the inclusion of additional parts such as bearing rings, spheres, etc.
The present invention relates to improvements for reducing the friction that is encountered by an armature of an EEGR valve when an electric control signal applied to the valve commands armature movement for changing the extent to which the valve restricts exhaust gas recirculation. The invention arises through the discovery that radial components of the magnetic field that act on the armature create radial force components that affect the friction that the armature encounters as it moves axially within a nonmagnetic sleeve that guides the axial armature motion. The extent to which the centerline of the armature departs from concentricity with the centerline of the electromagnet coil that creates the magnetic field also affects the friction. The invention provides a solution that reduces the influence of radial components of the magnetic field on the armature, and consequently diminishes the frictional forces that the armature encounters as it travels within the sleeve. It is believed that these reductions in friction can provide meaningful improvements in valve response and accuracy without the inclusion of additional parts such as bearing rings, and without significantly altering the functional relationship of axial force versus coil current.
While establishing the best concentricity of the armature to the coil and associated stator structure is also important in reducing armature friction, the invention is able to reduce armature friction in conditions of less than perfect concentricity. The invention accomplishes this by providing a minimum air gap between the stator structure and the armature, the minimum air gap being provided by spacing a hub of a stator pole piece from a non-ferromagnetic guide sleeve along a region of mutual axial overlap. Various specific embodiments are disclosed.
One general aspect of the present invention relates to an emission control valve for controlling flow of gases with respect to combustion chamber space of an internal combustion engine. The valve comprises a housing having a passage that has an inlet port for receiving gases, an outlet port for delivering gases to the combustion chamber space, and a valve element that is selectively positioned by an electric actuator to selectively restrict the passage. The actuator comprises a solenoid having an electric coil, stator structure, and a positioning mechanism, including an armature that is selectively positionable along an axis, for selectively positioning the valve element. The stator structure and the armature cooperatively form a magnetic circuit in which the coil, when energized by electric current, creates magnetic flux for selectively positioning the armature along the axis. The stator structure is separated from the armature by an air gap that includes a non-ferromagnetic guide sleeve that is in surface-to-surface contact with the armature for guiding armature motion along the axis. The guide sleeve and the stator structure are mutually overlapping along a region of the axis and are fit to substantial mutual concentricity with the axis, and at that region, the air gap includes a minimum air gap provided by radial spacing between the stator structure and the guide sleeve.
Another general aspect of the present invention relates to an automotive vehicle emission control system that includes a valve, as described above, for controlling flow of gases with respect to combustion chamber space of an internal combustion engine that powers the vehicle.
Still another general aspect of the present invention relates to a method of reducing friction between an armature and a non-ferromagnetic guide sleeve of an electric actuator of an automotive vehicle emission control valve wherein the guide sleeve has surface-to-surface contact with the armature for guiding armature motion along an axis while separating the armature from stator structure of the actuator by an air gap. The method comprises disposing the guide sleeve and the stator structure in mutually overlapping axial relation along a region of the axis, fitting the guide sleeve and the stator structure to substantial mutual concentricity with the axis, and at the mutually overlapping region, providing a minimum air gap by radially spacing the stator structure from the guide sleeve.
The foregoing, and other features, along with various advantages and benefits of the invention, will be seen in the ensuing description and claims which are accompanied by drawings. The drawings, which are incorporated herein and constitute part of this specification, disclose a preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.